1. Field of the Invention
The present invention relates to a semiconductor device evaluation apparatus and particularly, to a semiconductor device evaluation apparatus for evaluating an electromagnetic near-field strength of a semiconductor device. The present invention further relates to a magnetic field sensor suitable for use in the semiconductor device evaluation apparatus.
2. Description of the Prior Art
EMI (electromagnetic interference) evaluation of electronic equipment is to measure an emitted far-field of the electronic equipment according to measurement methods stimulated in various kinds of standards and evaluate whether or not an emission quantity meets a standard. If the standard is not met, further detailed evaluation is performed at levels of a case and a print circuit board of the electronic equipment as evaluation objects in order to specify a problematic part in the equipment.
As a fundamental evaluation method, there can be named a method in which electrical parameters such as a current, a voltage and an electromagnetic near-field and the like at parts of an object for evaluation are measured by proper means and a part which has a possibility to cause a problem in terms of electromagnetic compatibility is thus specified. For example, in Japanese Patent Application Laid-Open No. 4-230874, there is disclosed a method in which a two-dimensional electromagnetic strength measurement apparatus is employed, a print circuit board built in electronic equipment is extracted therefrom, a magnetic field sensor is disposed in the vicinity of the print circuit board, a two-dimensional magnetic field distribution is measured in a plane which is parallel to the board and it is eventually evaluated that a part where a high magnetic strength is measured has a high possibility of being a noise source.
In such a conventional example, in many cases, there has been adopted a method In which, at first, a problematic part and a mechanism of a problematic circuit function are selected by narrowing candidates from a list thereof according to experiences and expertise of a person in measurement and an optimal EMC countermeasure is attained. For a countermeasure in an EMC, it is important to conduct non-contact measurement in order to suppress, to the lowest level possible, an electrical influence on a circuit function of the electronic equipment which is an evaluation object. When a semiconductor device itself (for example, a semiconductor package) as an object for evaluation is, in a non-contact manner, measured to specify an internal problematic part as in the case of electronic equipment, there arises a necessity for an electromagnetic sensor with a spatially high resolving power.
However, a practical electromagnetic sensor adaptable for a semiconductor device has not been known.
As a noise evaluation method of a semiconductor device, there is available a document: xe2x80x9cElectromagnetic Emission (EME) Measurement of Integrated Circuits, DC to 1 GHzxe2x80x9d IEC 47A/429/NP NEW WORK ITEM PROPOSAL, 1996.2, published by IEC in which a measurement method for emission noise from a semiconductor device is shown. Besides, there is also available a document: xe2x80x9cElectromagnetic Compatibility Measurement Procedures for Integrated Circuitsxe2x80x9d IEC 47A/428/NP NEW WORK ITEM PROPOSAL, 1996.2, published by IEC in which a measurement method for conduction noise which occurs in each pin of a semiconductor device is shown.
Two measurement methods for an emission noise from a semiconductor device package are shown. One will be shown below. A semiconductor device which is an object for evaluation is mounted on a surface of a print circuit board and peripheral circuitry for operating the semiconductor device is constructed on the rear surface thereof. The print circuit board is fixed on a plane in the top portion of a TEM cell so that a surface of the print circuit board on which a semiconductor device is mounted resides in the inside of the TEM cell. One end of the TEM cell is constructed as a reflection-free terminal and the other end connected to a spectrum analyzer, and thereby emission noise from the semiconductor device only can be measured excluding influences from the peripheral circuitry.
A second method will be shown below. A semiconductor device as an object for evaluation is mounted on a surface of a print circuit board and peripheral circuitry for operating the semiconductor device is constructed on the rear surface thereof. The print circuit board is disposed with the surface on which the semiconductor device is mounted facing upward and a shielded loop constructed from a semi-rigid coaxial cable is arranged above the print circuit board. The vicinity of the semiconductor device is scanned with the shielded loop along a plane parallel to the print circuit board by a scan mechanism and thereby emission noise from the semiconductor device only can be measured. In this case, the maximal value of outputs at measurement sites is evaluated as a problematic site to specify.
Then, a measurement method for conduction noise which occurs in each pin of a semiconductor device package will be shown below. A structure comprises a test board for mounting a semiconductor device which is an object for evaluation and a main board for connecting the test board and a spectrum analyzer thereby. The semiconductor device is mounted in the center of the circular test board and the test board is attached to the main board in the center thereof. Interconnects are provided on each of the two boards radially toward the outside of the board and conduction noise from the pins of the semiconductor device is measured by the spectrum analyzer which is connected to the pins through connectors of a coaxial type mounted in the vicinity of the outer periphery of the main board.
As other examples, the following methods are named. For example, in Japanese Patent Application Laid-Open No. 64-65466, there is disclosed an identification method for an electromagnetic field noise generating part in which a reference plane is imagined which intersects electronic equipment, an arbitrary plane which is in parallel with the reference is scanned with an antenna, strengths of electromagnetic field noise and noise generating sites are sampled, and thereby a generation distribution map for electromagnetic noise of the electronic equipment as viewed from the arbitrary plane set in advance is expressed in the form of a contour map. Besides, in Japanese Patent Application Laid-Open No. 5-119089, there is disclosed an electromagnetic radiation visualization apparatus, in which a variable-length dipole antenna 3 of a measurement unit I is fixed in length which matches a measurement frequency and the antenna 3 is moved by a three-dimensional movement mechanism 4 in an anechoic electromagnetically chamber 7 while scanning. At this point, the interior of the electromagnetically anechoic chamber 7 is optically made dark and a brightness of a lamp 2 which is proportional to an electric field strength at each measurement site is recorded by a stereocamera 5 with exposure. Furthermore, in Japanese Patent Application Laid-Open No. 6-58970, there is disclosed an invention having an object to provide an EMI measurement apparatus which can three-dimensionally measure noise along X-Y-Z directions on the front side of a print wiring board on which electronic parts with much of unnecessary radiation are mounted, and which can two-dimensionally measure noise along X-Y directions on the rear side thereof. This is an EMI measurement apparatus which has a construction in which a print wiring board is set to an antenna for measuring an interference in which winding coils are arranged in an array and a magnetic near-field prove is mounted on the fore end arm of a robot which can be driven along X Y-Z directions on the front side of the print wiring board in order measure a noise generating source of the print wiring board on which an electronic part which is rich in unnecessary radiation is mounted, whereby a distribution of magnetic field strengths in unnecessary radiation on both sides, front and rear, is measured. In addition, in Japanese Patent Application Laid-Open No. 9-80098, there is disclosed an EMC probe, by which a spatial resolving power is increased and a measurement band region is sufficiently secured. This comprises a flexible board whose surface is insulated and a winding 11 with a single turn or a plurality of turns for detecting a magnetic near-field vector of an object for measurement, while being disposed obliquely, the winding being constructed from a metal thin film formed in a plane on the board.
Problematic points of a measurement method for emission noise from a semiconductor device package will be described below. First of all, problematic points of a method using a TEM cell will be described.
A first problematic point is that there is available no detailed standards for designing of a print circuit board on which a semiconductor device is mounted and thus an evaluation result depends on a design of the print circuit board. Besides, since a print circuit board on which a semiconductor device is mounted is square, there can be four ways to mount the semiconductor device, but a result is different according to a way to be mounted.
The reason why is considered that an electromagnetic wave emitted from a surface of a print circuit board on which a semiconductor device is mounted has a polarized wave and a pin position whose emission is large in quantity is changed, whereby emission characteristics are largely changed.
A second problematic point is that if a quantity of emission noise exceeds a tolerable level, though the emission noise can correctly be measured, a countermeasure is required. However, this method is very hard to specifically locate a problematic site.
The reason why is that since the semiconductor device is present in the TEM cell, it is impossible to correctly confirm what part of the semiconductor device has a problem.
A third problematic point is that a print circuit board is required to be prepared for each semiconductor device for evaluation, which entails cost in terms of time and economy.
A fourth problematic point is that since the semiconductor devices are evaluated under constant conditions, evaluation results have chances in which the results are not effective for use conditions by a user.
In addition, problematic points of a method using a shielded loop will be described.
A first problematic point is that there Is available no detailed standards for designing of a print circuit board on which a semiconductor device is mounted and thus an evaluation result depends on a design of the print circuit board.
The reason why is considered that an electromagnetic wave emitted from a surface of a print circuit board on which a semiconductor device is mounted has a polarized wave and thereby emission characteristics are largely changed.
A second problematic point is that if a quantity of emission noise exceeds a tolerable level, though the emission noise can correctly be measured, a countermeasure is required. However, this method is very hard to specifically locate a problematic site.
The reason why is that a small-sized type is hard to be realized since the shielded loop is prepared by a semi-rigid coaxial cable and as a result, a structure has an insufficient spatial resolving power and it is impossible to correctly confirm what part of a semiconductor device has a large emission.
A third problematic point is that a print circuit board is required to be prepared for each semiconductor device for evaluation, which entails cost in terms of time and economy.
A fourth problematic point is that since the semiconductor devices are evaluated under constant conditions, evaluation results have chances in which the results are not effective for use conditions by a user.
Furthermore, problematic points of a measurement method for conduction noise which occurs in each pin of a semiconductor package will be described below.
A first problematic point is that since electrical connection between the test board and the main board depends on point contact formed by pressure bonding of metal pin, transmission characteristics come to be in disorder under a high frequency band close to 1 GHz.
The reason why is considered that an impedance becomes discontinuous in the point contact portion.
A second problematic point is that a test board has to be newly prepared for each semiconductor device for evaluation, which entails cost in terms of time and economy.
A third problematic point is that since the semiconductor devices are evaluated under constant conditions, evaluation results have chances in which the results are not effective for use conditions by a user.
A fourth problematic point is that evaluation of a semiconductor device which requires circuitry with a large construction is hard to be performed because of requirement for a large space.
In this way, conventional examples have had inconveniences that, firstly, it is hard to correctly measure emission noise of a semiconductor device and secondly, even if emission noise can be measured, it is impossible to specify what part in the semiconductor device is problematic.
It Is an object of the present invention to provide a magnetic field sensor by which the above described inconveniences which conventional examples have had are improved and especially, emission noise of a semiconductor device can correctly be measured. It is another object of the present invention to provide a semiconductor device evaluation apparatus with good workability and high reliability which can perform EMI evaluation of a semiconductor device.
The present invention, therefore, has a configuration which comprises: an electromagnetic field measurement unit for measuring an electromagnetic field distribution emitted from a semiconductor device; an electromagnetic field distribution extracting unit for extracting a distribution of an electromagnetic field higher than a threshold value determined in advance and positional information of the distribution from an electromagnetic field distribution of a semiconductor device which is measured by the electromagnetic field measurement unit; and a part specifying unit for specifying a part of an object for measurement an electromagnetic field emitted from which is high among parts of the object for measurement based on the positional information of the electromagnetic field distribution which is extracted by the electromagnetic field distribution extracting unit. This allows the objects described above to be attained.
The electromagnetic field measurement unit measures an electromagnetic field distribution which is emitted from a semiconductor device. Then, the electromagnetic field distribution extracting unit extracts a distribution of an electromagnetic field higher than a threshold value determined in advance and positional information of the distribution from an electromagnetic field of the semiconductor device. The positional information may be, for example, a distribution image in which information on whether or not an electromagnetic field exceeds the threshold is stored in a pixel corresponding to the information. The part specifying unit specifies a part an electromagnetic field of whose emission is high based on the positional information of the electromagnetic field distribution. For example, a part of a semiconductor device such as an interconnect or a lead frame is specified. Thus, evaluation of an electromagnetic field emitted from the semiconductor device is effected.